Sorption and transport of CO₂ in poly(ethylene terephthalate) crystallized by sorption of high‐pressure CO₂

Sorption and permeation of CO 2 in poly(ethylene terephthalate) crystallized by sorption of high‐pressure CO 2 were examined below 1 atm at temperatures from 15 to 65°C. A large solubility and a high permeability of CO 2 in this specimen were observed compared to poly(ethylene terephthalate) crystallized by thermal annealing to a similar degree. A large unrelaxed volume is expected to be left in the specimen after removal of high‐pressure CO 2 compared to the data of other PET samples. The thermal history during the measurements up to 65°C, which causes relaxation of the specimen, was shown to decrease CO 2 solubility. On the other hand, permeation data after annealing show not only decreased permeability but also increased apparent diffusivity. The results mean a lower mobility of gases sorbed in the unrelaxed volume than that of ordinarily dissolved gases, which corresponds to the partial immobilization model.